please help! only 3 out of 4 gpus detected

amd1361

hi
I really need your help guys as i am struggling to make my fourth gpu to be detected by my GIGABYTE F2A88X-UP4 FM2+.
I have put one of my gpus (sapphire rx 470 nitro) into pciex8 and the rest (using 1x to 16x risers)into pciex1-1,pciex1-2 and pciex1-3.
when i go to windows just 3 cards are detected and one of the pciex1 is not detected at all.(my gpus,mainboard and cables are 100% ok)
please help me. is there anything in the bios I can change to make the fourth one come to life.
here is the motherboard pic

cviper

if its windows 7 only 3 would be detected cuz its need registry hack if its windows 10 it should work from the start , if not reset the bios and try again.